Apparatus for tuning mechanically resonant elements



June 20, 1967 H. J. NELSON 3,326,067

APPARATUS FOR TUNING MECHANICALLY RESONANT ELEMENTS Filed Aug. 2, 1965 I5 Sheets-$hest 1 Z mg SEE (DU) 0 D.

MEANS IN VEN TOR. HAROLD J. NELSON ATTORNEYS June 20, 1967 H. J. NELSON 3,326,067

APPARATUS FOR TUNING MECHANICALLY RESONANT ELEMENTS Filed Aug. 2, 1965 3 Sheets-Sheet 3 (iii 7 AIR PRESSURE /5/ SOURCE //7 m ONE SHOT FIG 4 IN VEN TOR. HAROLD J. NELSON ATTORNEYS United States Patent 3,326,067 APPARATUS FOR TUNING MECHANICALLY RESONANT ELEMENTS Harold J. Nelson, Santa Ana, Calif., assignor to Collins Radio Company, Cedar Rapids, Iowa, a corporation of Iowa Filed Aug. 2, 1965, Ser. No. 476,284 12 Claims. (Cl. 77-5) This invention relates generally to means for automatically tuning mechanically resonant elements and, more particularly, to an automatic means for tuning small metallic discs used in mechanical filter devices.

Mechanical filters have become widely used in highquality electronic gear. Such mechanical filters employ a plurality of metallic discs which are secured together in a stack arrangement and each of which has a natural resonant frequency. These discs are fastened together by supporting rods and function to provide an overall frequency response characteristic, superior in many ways to the characteristic of other type filters.

In the manufacture of mechanical filters, the tuning of each disc is important and quite critical. Such tuning is done generally in the following manner. The disc is formed initially to have a natural resonant frequency just a little above the ultimately desired natural resonant frequency. Each disc is then individually excited into its natural resonant frequency state and such initial frequency measured. A portion of the disc is then removed, as by a drilling operation for example, in order to lower the natural resonant frequency towards the desired frequency. After the first drilling the disc is again tested for natural resonant frequency and if such frequency is still above the desired frequency, a second drilling is effected. This alternate drilling and testing continues until the natural resonant frequency of the disc is at the desired value (i.e., within the allowable tolerances). Obviously, if the natural resonant frequency of the disc was below the desired value to begin with, the disc is discarded, since it is not feasible to add material to the disc, which is necessary to increase the natural resonant frequency. Thus, the reason for initially forming the disc to be a little above the desired frequency is more apparent.

In the prior art method of manufacturing discs, the above operations have been done manually. That is to say, an operator will pick up an individual disc and insert it in a machine which will excite the disc and indicate what the natural resonant frequency is. If such frequency is too high, the operator will press a button and cause a drill to remove a certain portion of the disc. The operator then again tests the natural resonant frequency of the disc to determine if additional drilling is required.

It is a primary object of the present invention to provide an automatic means for alternately checking the resonant frequency of such discs and removing a portion of such discs by drilling means until the desired natural resonant frequency is obtained.

A second object of the invention is an automatic means for tuning mechanical filter discs, wherein no operator is necessary other than to load the discs into a supply bin.

A further object of the invention is an automatic disc tuning means which will function to discard those discs whose frequency is too low or too high to be corrected, and to automatically tune and sort those discs which are tunable.

A fourth object of the invention is the improvement of means for tuning mechanically resonant elements, generally.

In accordance with the invention there is provided a large, fiat, circular plate mounted on a suitable fiat supporting surface. This plate has a plurality of equally 3,326,067 Patented June 20, 1967 spaced semicircular slots cut in the outer edge thereof, of a size and shape suitable for receiving and holding the discs. Means are provided to cause the plate to rotate in discrete angular steps so that each slot in the periphery of the plate will successively come to rest at a first given position on the supporting platform.

Feeding means are provided to supply a single disc into each slot at said given point on the periphery of the plate as each succeeding slot is moved into said first given position. At another stopping position (hereinafter called a testing station) for the discs, there is provided both a means for resonating and measuring the natural resonant frequency of the discs, and also a means for removing a portion of the disc being tested; such as a drilling means. Control or selecting means are provided to respond to the natural resonant frequency of the disc to sort the discs into three bins. More specifically, such frequency responsive means functions to operate relays which opens one of the three bins to the disc tested. The three bins thus contain three different groups of discs: those in which the frequency is too low; those in which the frequency is too high to be corrected; and those in which the frequency has been successfully adjusted.

In accordance with a feature of the invention, there is provided a control circuit comprising a coil positioned underneath the test position of the discs to be tested. When this coil is excited it creates a magnetic field which shocks the disc being tested into its natural resonant mode of vibration. The exciting coil has a capacitor associated therewith to provide a natural resonant frequency equal to that desired in the mechanical discs. If the frequency of the mechanical discs varies from the desired frequency, a resultant overall frequency of the system including the disc, the exciting winding, and the capacitor will result which will be different from the desired frequency. Filtering circuits are provided to measure this resultant frequency and if it is either too high or too low, a signal is generated which will cause the holding plate to rotate to discard the defective disc, and move a new disc into the testing position. If the disc is tunable the drilling means is energized.

Immediately before a defective disc is discarded, certain logic means, res onsive to various filter outputs indicating a defective disc, are energized to open the proper bin into which the defective disc is dropped. Similarly, when the disc is tuned to the proper frequency, a filter responds to the resultant overall frequency of the disc, coil, and capacitor to move the holding plate and eject the tested disc into a bin employed to hold discs within the accepted tolerances. Here, again, the logic means are responsive to cause said bin to be selected.

The above-mentioned and other objects and features of the invention will be more fully understood from the following detailed description thereof when read in conjunction with the drawings in which:

FIG. 1 is a simplified side view illustration of the overall concept of the invention;

FIG. 2 is a simplified top view illustration of the invention;

FIG. 3 is a combination plan view, block diagram, and schematic diagram of the control means of the invention; and v FIG. 4 is a combination schematic diagram and plan view of the drill and its controls.

Referring now to FIG. 1, there is shown a feeding means 10 for supplying discs to the tuning means. The feeding means 10 is a standard commercial item of a type No. CBOB, Style 1911, manufactured by the Syntron Company of Homer City, Pa. Since it is a standard commercial item it will not be described in detail herein. Basically, the feeder 10 is a bowlshaped arrangement in which a plurality of discs are placed. The center of the bowl is at a higher level than the edges of the outside perimeter so that vibrating the bowl will cause the discs to move to the outer periphery thereof by gravity force. The discs, indicated generally in FIG. 1 by reference character 60, are then fed from the perimeter of the bowl into a chute 11, in a single file as indicated in FIG. 2. An electromagnet 61, which may be energized by battery 62 or, alternatively, a permanent magnet, functions to pull the disc into the particular slot of rotating plate 14, which slot is at that time positioned at the foot of ramp 11. In FIG. 2 a

disc 64 is shown entering slot 63. Other discs such as discs 65, 66, and 67 have been positioned in slots on preceding cycles of the operation as the rotating plate 14' moves in a clockwise direction.

Still referring to FIG. 2, each time the rotating plate 14' stops, a disc in one of the slots will come to rest at a position as represented by disc 68. This particular position is the testing position. Over this testing position is poised the bit 33 of a drill 32, as shown in FIG. 1. Underneath the disc in such test position is a winding coil 29 (FIG. 1) which corresponds to the coil 29' in FIG. 3. Such coil 29 is employed to shock the disc being tested into its natural mode of vibration.

In a manner to be described in connection with FIG. 3, if the disc being tested has a frequency above the desired frequency (although not too far above), the drill 32 is caused to automatically lower the bit 33 onto the disc being tested and to drill a small, predetermined amount of material from the disc. The drill 32 then rises and the winding 29 is again energized to shock the disc into vibration. If the frequency of vibration, detected in a manner to be described in detail later, is still too high, the drill is again lowered to remove more material from the disc. The disc is then again shocked into vibration and its frequency checked. Such process is continued until the frequency of the disc falls within the accepted predetermined range, at which time the rotating plate 14 is caused to rotate to its next angular position and the tested disc dropped into the bin 28 which holds the tuned discs.

It will be noted that there are two other bins identified by reference characters 26 and 27 and marked low and high, respectively. At the top ends of the separators 18 and 19 forming the three bins are two magnetically operated deflectors 21 and 24. Such deflectors 21 and 24 are operated by the rotary solenoids 20 and 23, shown symbolically in FIG. 1.

If the frequency of the disc being tested is too low, then both of the rotary solenoids 20 and 23 will be operated so that the deflectors 21 and 24 will be in the positions shown by dotted lines 22 and 25, respectively.

On the other hand, if the frequency of the disc being tested is so high that it cannot be satisfactorily reduced, only the rotary solenoid 23 will be energized so that defiector 21 will be in its vertical position, as indicated, and deflector 24 will be in the position as indicated by dotted line 25. The disc being tested will then be deflected into bin 27, which is marked high in FIG. 1. If the disc being tested has been adjusted satisfactorily, neither rotary solenoid 20, nor rotary solenoid 23 will be energized, so that both deflectors 21 and 24 will be in their upright positions. The disc will then be dumped into bin 28, which is marked tuned in FIG. 1.

The drill 32 is supported by arm 31 which, in turn, is mounted on post 30. A clamp 36 functions to secure the radial swing of arm 31 on post 30, while the height adjustment 35 is employed to secure the height of arm 31 on post 30. Lever 34 is utilized to grip the drill 32 securely within arm 31.

It is to be noted that drill 32 is of a construction enabling it to lower itself onto the disc being tested for a given interval of time and with a certain pressure so that a predetermined amount of material Will be removed from the disc. Such a drill is available as a standard commercial item. It is manufactured by the Dumore Company of Racine, Wis., and is identified as Series 24, Catalog No. 24-051.

The rotating plate 14 is mounted on a shaft 15 and rigidly secured thereto by a suitable holding means 41. The other end of shaft 15 is mounted in shaft positioning means 16 which functions to rotate shaft 15 and, conse quently, rotating plate 14, by predetermined angular in crements which will position successive slots in the periphery of rotating plate 14 at the base of the ramp 11 and also at the test position 68 of FIG. 2.

Referring now to FIG. 3, there is shown a combination block diagram, schematic diagram, and structural diagram of the control portion of the system. The pawl and ratchet arrangement identified by reference characters 82, 83, and 84 is a mechanical means by which the rotating plate 14 in FIGS. 1 and 2, is rotated in discrete angular steps to properly position the mechanical discs being tested. In the general operation, arm 84 is actuated by relay 81, when energized, to cause pawl 83 to withdraw from the teeth of ratchet 82. At the same time, the other end 152 of arm 84 will engage a tooth, such as tooth 151, to cause ratchet 82 to rotate so that the tooth gap 153 will fall under pawl 83. When relay 81 is de-energized the pawl 83 will be pulled into tooth gap 153 by spring means 86 to position ratchet 82 quite precisely. It is to be noted that pawl arm 84 pivots on a suitable pivot means 85.

Energization of the pawl and ratchet means by relay 81 occurs when a signal appears at the output of any of the filters 69, 70, or 71. The filters 69, 70, and 71 will each produce an output signal when the frequency of the mechanical disc being tested is either too low, too high to be corrected, or when it has been tuned to within the proper frequency range, respectively.

The winding 29 corresponds to the winding 29 in FIG. 1, and is positioned in series with capacitor 65. The overall resonant frequency of the coil 29' the capacitor 65, and the mechanical disc being tested will vary over a frequency range depending upon the natural resonant frequency of the mechanical disc. A portion of such overall resonant frequency or signal is supplied through coupling capacitor 66 to amplifier 67, and thence in parallel to the three filters 69, 70, and 71.

If such overall resultant frequency is below a certain predetermined value, there will be an output signal from low-pass filter 69, which signal will pass through OR gate 72 to energize pulse generator 79. Similarly, if the overall resultant frequency is so high as to indicate that the disc is not tunable to the desired frequency, the signal across capacitor will pass through high-pass filter and OR gate 72 to energize pulse generator 79.

The third alternative occurs when the mechanical disc has been properly tuned. Under such circumstances, the. signal across capacitor 65 will be supplied through coupling capacitor 66, amplifier 67, notch filter 71, and OR gate 72 to pulse generator 79.

In response to output signals from any of the three filters 69, 70, and 71 through OR gate 72, the pulse generator 79 will generate a pulse to energize relay winding 81 and, consequently, cause ratchet wheel 82 to step forward one position.

As the ratchet wheel 82 steps forward it will turn the rotatable plate 14 since it is rigidly secured thereto through shaft 15 of FIG. 1. The disc, which has just been tested, will then be routed into one of the three bins 26, 27, or 28. In FIG. 3 the rotary solenoids 20' and 23 correspond to the rotary solenoids 20 and 23 of FIG. 1 and can be seen to be energized by solenoid means 77 and 78, respectively. In FIG. 1 if the frequency of the disc being tested is too low, it can be seen that the disc must be dropped into bin 26 and that both rotary solenoids 20 and 23 must be energized. To perform this logic the output of low-pass filter 69 of FIG. 3 is connected directly to solenoid winding 77 through lead 74, and to solenoid winding 78 through lead 75 and diode 76. The diode 76 functions to isolate the output of high-pass filter 70 from relay winding 77, as will be seen in the following paragraph.

If the frequency of the disc being tested is too high to permit tuning, then the disc must be dropped into bin 27, which is accomplished by energizing only solenoid 23 so that separator 24 assumes the position indicated by dotted line 25 (FIG. 1). To produce such a condition, the output of high-pass filter 70 in FIG. 3 is passed through the lead 73 to energize winding 78 of rotary solenoid 23'.

If the mechanical disc is properly tuned, neither the rotary solenoid 20 or 23 of FIG. 1 are energized, and the disc is dropped into tuned bin 28. Accordingly, in FIG. 3, the output of the notch filter 71 is supplied only to the OR gate 72, and thence to pulse generator 79, and does not function to energize either the windings 77 or 78.

In the event that the disc falls within the tunable range but is not yet tuned to the tolerance desired, some means is needed to so indicate such a situation. The filter 105 fills this need and is constructed to respond to frequencies lying between the desired frequency and the frequency above which it is felt the disc cannot feasibly be tuned. In other words, the frequency band of filter 105 constitutes that band of frequencies in which the resonant frequency of a disc must lie in order to be correctable to the desired frequency.

The circuit is designed so that the rotary solenoids 20' and 23 will operate before the ratchet wheel 82 turns. Thus, as ratchet wheel 82 and the rotary plate 14 of FIG. 1 turn, the rotary solenoids 20' and 23' are already activated, if necessary, and the disc will fall into the proper bin.

The pulse generator 79 is designed to generate a pulse for a predetermined interval of time, which continues even after the energizing signal supplied thereto through OR gate 72 has terminated. The reason for this is as follows.

The energization of the coil Winding 29', which excites the disc 103 into resonance, is generated from the output of one-shot multivibrator 102. However, the resonant condition of disc 103 might not last long enough to produce energization of relay winding 81 through the appropriate filters 69, 70, or 71. Consequently, the pulse generator 79 is utilized to assure operation of the relay 81.

It is to be noted that one-shot multivibrator 102 can be energized through OR gate 101 from two sources. One of these sources isthe pulse generated when the contacts 91 are made after the ratchet wheel 82 has stepped forward one position. The battery 104 will then produce a pulse through OR gate 101 to energize multivibrator 102 and thus initiate the testing of the particular disc in the test position. If such disc lies in' the tunable range an output signal will appear at the output of filter 105 and will be supplied back to input 98 of flip-flop 95, thereby producing a signal on output lead 96 of said flip-flop circuit. Such output signal is supplied to the drill control circuit to initiate a cycle of drilling. As discussed above, a cycle of the drilling consists of the drill coming down on the disc being tested to remove a sinall portion thereof, and thereby reduce the resonant frequency of the disc. The drill then withdraws into its upper position and will cause a pulse to be supplied back to input 97 of the flip-flop 95.

The pulse supplied to the input 97 of the flip-flop resets the flip-flop to produce an output signal on the reset output terminal 99. The leading edge of such reset output signal energizes one-shot multivibrator 102 which, in turn, energizes the testing resonant circuit, including coil 29' capacitor 65 and disc 103. A portion of the resonant frequency signal is supplied through capacitor 66, amplifier 67, to the four filters 69, 70, 71, and 105.

If additional adjustment of the disc is required an output signal will appear on the output of filter 105 to set flip-flop 95 and thus initiate another cycle of drilling and testing.

When the disc is fully tuned, an output signal will appear at the output of the notch filter 71 to energize relay 6 81 and step the pawl and ratchet to its next position, opening and closing the contacts 91 during the process. The closing of the contacts 91 will energize the one-shot multivibrator 102 to initiate testing of the next disc.

Referring now to FIG. 4, there is shown a more detailed diagram of the drill and the controls for causing the drill to come down on a disc being tested and remove a portion thereof.

In FIG. 4 the casing of the drill 32' is held firmly in the arm 31 as shows in FIG. 1. The main shaft 119 of the armature is keyed to the armature windings 121 to permit a longitudinal movement of the shaft 119 with respect to the windings 121 while locking shaft and windings together in an angular direction. Bearing 120 provides a means for rotating shaft 119 in housing 32. Field windings 122 are provided within housing 32'.

The longitudinal movement of the shaft 119 is controlled by air pressure means supplied to cavities 116 and 117, which form a cylinder containing a piston 118. The shaft 119 is rotatable freely within piston 118 due to the ball bearing support 150. A sleeve 123 is secured rigidly to piston 118, and at its lower end contains a ball bearing means 141 to facilitate the rotation of the main shaft 119. It should be noted, specifically, that piston 118 and its attached sleeve 123 is keyed in some suitable manner to housing 32' so that the piston and sleeve will not rotate. a

Air pressure from source 111 is supplied to the upper chamber 116 and the lower chamber 117 through ducts 112 and 113, respectively. The pressure in the lower chamber 117 is constant and, in the absence of a greater pressure in the upper chamber 116, will cause piston 118 to rise to its upper position. Such upper position is determined by the position of threaded stop 142, which is secured to some stable reference point through arm 142A.

When it is desired to cause the bit 33' to be lowered onto a disc, 21 signal is supplied to timing circuit through lead 96', as discussed in connection with FIG. 3. The timing circuit, which may be a one-shot multivibrator, functions to energize winding so that the solenoid piston 114 is raised to permit pressurized air flow from source 111 through duct 112 and into the upper chamber 116. The air pressure source 111 is constructed so that the air pressure through duct 112 is greater than that through duct 113. Thus, when piston 114 is raised, the piston 118 is forced downward, bringing with it armature shaft 119 and bit 33 to drill the disc being tested. The amount of time (dwell) that the drill is lowered onto a disc is determined by the tim constant in timing circuit 110.

In order to regulate the acceleration, velocity, and pressure of the bit 33' as it comes down on the disc being drilled, there is provided a counteracting piston arrangement designated generally by reference character 143. This piston arrangement 143 (or check valve arrangement) comprises piston 125, a housing 126, a chamber 127, and an orifice 144. Leading into the chamber 127 is an air duct 129 with a solenoid piston valve 145 therein. When the winding 130 is de-energized, the piston is in its lower position, and the duct 129 is closed. Thus, as the armature shaft 119 of the drill is lowered, the arm 124, which is secured rigidly to the sleeve 123, impinges against piston valve 125, forcing said piston valve downward. Thus, there is provided a counter force to the force causing the armature shaft 119 to move downward. The amount of such counter force is determined by the size of the orifice 144 in the chamber 127, through which orifice the trapped air escapes as the piston 125 lowers.

It is to be noted that the amount of drilling done is determined by the difference between the force pushing the bit 33 down and the counteracting force produced by the check valve 143. In the tuning of any given disc, however, two or more separate drillings might be necessary. In such a case the first drilling will function to push the check valve down a certain distance X. When the drill is raised again, prior to the second drilling on the same disc, the piston 125 will not rise back to its uppermost position since the winding 130 will not have been energized in the interim. Thus, when the drill is caused to come down on the disc a second time, said drill will travel downward through the distance X before engaging the piston 125. During the dwell of the second drilling, piston 125 will be pushed down another distance Y. If a third drilling is required, the drill arm 124 will move downward through the distances X and Y before engaging the piston 125.

At the completion of tuning of the disc a signal will be received on the lead 80' (see FIG. 3) which signal will energize multivibrator 131, thereby energizing Winding 130 to raise the solenoid piston 145. When piston 145 is raised, pressurized air from source 111 is permitted to enter chamber 127 and push the piston 125 to its uppermost position in preparation for the next cycle of operation.

It is to be noted that the form of the invention shown and described herein is but a preferred embodiment thereof and that various changes may be made therein without departing from the spirit or scope thereof.

I claim:

1. Means for tuning mechanically resonant elements to a desired frequency comprising:

first feeding means for automatically feeding individual ones of said elements to a predetermined receiving station;

second feeding means constructed to receive and hold a plurality of said elements and to move said elements through a predetermined, continuous path, at equally spaced time intervals;

driving means constructed, when energized, to drive said second feeding means in discrete steps to cause each of the elements held therein to stop at the same locations as all the other elements held therein;

one of said stop locations comprising said receiving station;

said second feeding means constructed to receive one of said elements during each stop condition of said second feeder means;

testing station means located at a stop location of said second feeder means;

means for exciting said elements into resonance at said testing station;

cutting means constructed, when energized, to remove a portion of said element being tested;

storage means constructed to receive elements after testing; and

frequency responsive mean responsive to the frequency of the element being tested to selectively energize said cutting means or said driving means, to tune said element or drive said second feeder means and cause said element to enter said storage means.

2. Tuning means in accordance with claim 1 in which said cutting means comprises:

drilling means, with first control means, responsive to the resonant frequency of the element being tested, Within a particular range of frequencies, to cause said drilling means to remove a predetermined portion of the element being tested.

3. A tuning means in accordance with claim 2 in which said frequency responsive means comprises:

second control means responsive to a signal derived from the resonating element being tested to energize said driving means when the frequency of said signals is in a first band of frequencies indicating acceptable tuning of said element or in second bands of frequencies indicating the element cannot be satisfactorily tuned.

4. A tuning means in accordance with claim 3 in which said storage means comprises:

first compartment means and second compartment means for receiving acceptable and nonacceptable elements, respectively;

and solenoid means responsive to signals within said first and second bands of frequencies of said element being tested, to selectively open said first or second compartments to receive said element.

5. A tuning means in accordance with claim 1 in which said frequency responsive means comprises:

control means responsive to a signal derived from the resonating element being tested to energize said driving means when the frequency of said signals is in a first band of frequencies indicating acceptable tuning of said element or in second bands of frequencies indicating the element cannot be satisfactorily tuned.

6. A tuning means in accordance with claim 5 in which said storage means comprises:

first compartment means and second compartment means for receiving acceptable and nonacceptable elements, respectively;

and solenoid means responsive to signals within said first and second bands of frequencies of said element being tested to selectively open said first or second compartments to receive said element.

7. Means for tuning mechanically resonant elements to a desired frequency comprising:

feeding means for automatically feeding individual ones of said elements to a predetermined receiving station;

rotary table means having a plurality of indentations formed in the outer perimeter thereof for holding said elements;

driving means constructed, when energized, to drive said rotary table means in discrete angular distances to cause each of said indentations to stop at said receiving station and receive one of said elements;

a testing station located at a predetermined point adjacent the periphery of said rotary table coincident with a stopping point of said indentations;

means for exciting said elements into resonance at said testing station;

cutting means constructed, when energized, to remove a portion of said element being tested;

storage means constructed to receive elements after testing;

frequency responsive means responsive to the frequency of the element being tested to selectively energize said cutting means or said driving means, and thereby tune said element or rotate said table to cause said element to enter said storage means.

8. Tuning means in accordance with claim 7 in which said cutting means comprises:

drilling means including first control means responsive to the resonant frequency of the element being tested, Within a particular range of frequencies, to cause said drilling means to remove a predetermined portion of the element being tested.

9. A tuning means in accordance with claim 8 in which said frequency responsive means comprises:

second control means responsive to a signal derived from the resonating element being tested to energize said driving means When the frequency of said signals is in a first band of frequencies indicating acceptable tuning of said element or in second bands of frequencies indicating the element cannot be satisfactorily tuned.

10. A tuning means in accordance with claim 9 in which said storage means comprises:

first compartment means and second compartment means for receiving acceptable and nonacceptable elements;

and solenoid means responsive to signals Within said first and second bands of frequencies of said element being tested, to selectively open said first or second compartments to receive said element.

9 11. A tuning means in accordance with claim 7 comprising:

control means responsive to a signal derived from the resonating element being tested to energize said driving means, when the frequency of said signals is in a first band of frequencies indicating acceptable tuning of said element or in second bands of frequencies indicating the element cannot be satisfactorily tuned. 12. A tuning means in accordance with claim 11 in which said storage means comprises:

first compartment means and second compartment 10 means receiving acceptable and nonacceptable elements; and solenoid means responsive to signals within said first and second bands of frequencies of said element being tested, to selectively open said first or second compartments to receive said element.

References Cited UNITED STATES PATENTS 3,230,614 1/1966 Rasch 29169.5

FRANCIS S. HUSAR, Primary Examiner. 

1. MEANS FOR TUNING MECHANICALLY RESONANT ELEMENTS TO A DESIRED FREQUENCY COMPRISING: FIRST FEEDING MEANS FOR AUTOMATICALLY FEEDING INDIVIDUAL ONES OF SAID ELEMENTS TO A PREDETERMINED RECEIVING STATION; SECOND FEEDING MEANS CONSTRUCTED TO RECEIVE AND HOLD A PLURALITY OF SAID ELEMENTS AND TO MOVE SAID ELEMENTS THROUGH A PREDETERMINED, CONTINUOUS PATH, AT EQUALLY SPACED TIME INTERVALS; DRIVING MEANS CONSTRUCTED, WHEN ENERGIZED, TO DRIVE SAID SECOND FEEDING MEANS IN DISCRETE STEPS TO CAUSE EACH OF THE ELEMENTS HELD THEREIN TO STOP AT THE SAME LOCATIONS AS ALL THE OTHER ELEMENTS HELD THEREIN; ONE OF SAID STOP LOCATIONS COMPRISING SAID RECEIVING STATION; SAID SECOND FEEDING MEANS CONSTRUCTED TO RECEIVE ONE OF SAID ELEMENTS DURING EACH STOP CONDITION OF SAID SECOND FEEDER MEANS; TESTING STATION MEANS LOCATED AT A STOP LOCATION OF SAID SECOND FEEDER MEANS; 